Analog front end device with temperature compensation

ABSTRACT

An analog front end device with temperature compensation is provided. The analog front end device comprises a bandgap voltage reference circuit, a clock generator, a temperature compensation circuit, one to three identical converting circuits and a Sync-on-Green circuit. The temperature compensation circuit is adapted to sense the temperature variations of the analog front end device and dynamically compensate the bandgap voltage reference circuit, the clock generator and the Sync-on-Green circuit as the temperature varies, which thereby controls the thermal drift in the analog front end device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an analog front end (AFE) device withtemperature compensation so as to solve a thermal drift due totemperature variation.

2. Description of the Related Art

Traditionally, AFE devices are being applied to two categories ofdisplay systems. First, an AFE device applied to a liquid crystaldisplay (LCD) controller without a decoder is used to receive threeanalog image signals R, G, B from a VGA card of a computer system.Second, an AFE device applied to a video decoder is used to receive asignal from a tuner or a DVD player. Wherein, the signal includes threekinds of video signals as follows. The first is a composite videosignal, often called a CVBS signal, which combines the luminance (Y) andchrominance (C) signals into a single channel. The second is a separatevideo signal separating the luminance (Y) and the chrominance (C)signals. The third is a component video signal which is split into threeseparate signals Y, Pr, Pb.

FIG. 1 shows a block diagram of a conventional AFE device. An AFE device100 comprises a bandgap voltage reference circuit 130, a clock generator140 and one to three identical converting circuits 150. Each convertingcircuit 150 further comprises a damper (101, 111, 121), an input buffer(102, 112, 122) and an analog to digital converter (ADC) (103, 113,123). Take the AFE device in the LCD controller, for example—threeconverting circuits 150 are required to convert three analog imagesignals R, G, B into three digital signals D1, D2, D3, respectively.Each converting circuit 150 uses the damper (101, 111, 121) to calibratethe DC level of the respective analog image signal, then uses the inputbuffer (102, 112, 122) to buffer the respective analog image signal andfinally supplies the respective analog image signal to the ADC (103,113, 123). The clock generator 140 receives either a horizontal sync(HS) signal or a vertical sync (VS) signal to provide a periodic clocksignal to the ADCs (103, 113, 123) for sampling. A reference voltageV_(ref), generated by the bandgap voltage reference circuit 130, isprovided to either the input buffer (102, 112, 122) for makingmodifications to both a gain and an offset voltage or the ADC (103, 113,123) for making modifications to a full-scale voltage or a bias current.

In general, the interior of an integrated circuit is divided into adigital circuit and an analog circuit. Normally, there is no thermaldrift in the digital circuit. By contrast, the thermal drift could occurin the analog circuit. For example, its voltage varies according to thetemperature and its frequency also varies according to the temperature.In applications of display system controllers (including the LCDcontrollers and the video decoders as mentioned above), users would likethe display system to have the same characteristic both at start-up (ata lower temperature) and after warm-up (at a higher temperature), e.g.,a consistent display color and a consistent optimum sampling phase ofthe ADC (103, 113, 123). In other words, it implies that the thermaldrift is not allowed to occur in the dampers (101, 111, 121), the ADCs(103, 113, 123), the clock generator 140 and related circuits (e.g., theSync-on-Green circuit).

Conventional analog circuit designs make use of a variety of techniques,such as generating either a voltage or a current independent of thetemperature, to eliminate the thermal drift in the dampers (101, 111,121), the ADCs (103, 113, 123), the clock generator 140 and relatedcircuits. However, these techniques have little effects on improving thethermal drift and waste hardware resources as well.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems, an object of the invention isto provide an AFE device with temperature compensation in order toeliminate a thermal drift in a display system due to temperaturevariation.

In accordance with one embodiment, the AFE device with temperaturecompensation comprises a bandgap voltage reference circuit, a clockgenerator, a temperature compensation circuit and one to three identicalconverting circuits. Each converting circuit receives at least oneanalog image signal and generates at least one digital signal. Eachconverting circuit which further comprises a clamper, an input bufferand an ADC is adapted to convert the analog image signal into thedigital signal. The temperature compensation circuit senses thetemperature of the AFE device. As the temperature of the AFE devicevaries, the temperature compensation circuit provides at least onecompensating signal to the AFE device so as to perform a dynamiccompensation on the AFE device, thereby controlling the thermal drift inthe AFE device.

According to a first embodiment of the invention, the temperaturecompensation circuit generates a first compensating signal and a secondcompensating signal to set related registers of the clock generator andthe bandgap voltage reference circuit respectively, thus varying theoptimum sampling phase, both the full-scale voltage and the bias currentof the ADC and both a gain and an offset voltage of the input buffer.According to a second embodiment of the invention, responsive to atemperature variation of the AFE device, the temperature compensationcircuit performs a dynamic compensation on the AFE device, e.g., thebandgap voltage reference circuit, the clock generator or theSync-on-Green (SOG) circuit, so as to control the thermal drift in theAFE device.

Further scope of the applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 shows a block diagram of a conventional AFE device.

FIG. 2 shows a block diagram of an AFE device with temperaturecompensation according to a first embodiment of the invention.

FIG. 3 shows a detailed block diagram of the temperature compensationcircuit of FIG. 2.

FIG. 4 is an example of the temperature compensation table according tothe first embodiment of the invention.

FIG. 5 shows a block diagram of an AFE device with temperaturecompensation according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The AFE device with temperature compensation of the invention will bedescribed with reference to the accompanying drawings.

FIG. 2 shows a block diagram of an AFE device with temperaturecompensation according to a first embodiment of the invention. Theinvention is disposed in a display system controller (including the LCDcontrollers and the video decoders as mentioned above). An AFE devicewith temperature compensation 200 comprises a temperature compensationcircuit 210, a bandgap voltage reference circuit 130, a clock generator140 and at least one converting circuit 150. The temperaturecompensation circuit 210 is adapted to sense the temperature of the AFEdevice 200. As the temperature of the AFE device 200 varies, thetemperature compensation circuit 210 sends a first compensating signalC1 and a second compensating signal C2 to the bandgap voltage referencecircuit 130 and the clock generator 140, respectively. Next, the bandgapvoltage reference circuit 130 adjusts the reference voltage according tothe first compensating signal C1 in order to avoid the thermal drift inthe reference voltage due to the temperature change. Besides, the clockgenerator 140 adjusts the clock signal according to the secondcompensating signal C2 in order to avoid the thermal drift in thereference voltage due to the temperature change and thus obtain anoptimum sampling phase. FIG. 3 shows a detailed block diagram of thetemperature compensation circuit of FIG. 2. The temperature compensationcircuit 210 comprises a temperature sensor 311 and a dynamiccompensation circuit 312. The temperature sensor 311 is adapted to sensethe temperature of the AFE device 200 and correspondingly generate asensing-resultant signal S_(O). With respect to the sensing-resultantsignal S_(O), the dynamic compensation circuit 312 performs a dynamiccompensation and then generates the first compensating signal C1 and thesecond compensating signal C2.

In the first embodiment of the invention, the dynamic compensationcircuit 312, implemented in firmware, can shortly retrieve correspondingparameters from a memory where a temperature compensation table 400(shown in FIG. 4) is pre-stored by using a lookup table if thetemperature varies. Note that the temperature compensation table 400 isillustrative only, as various changes and modifications thereof may bemade without departing from the spirit of the invention. The temperaturecompensation table 400 includes four columns: (1) temperature, (2)optimum sampling phase, (3) full-scale voltage of the ADC and (4) biascurrent of the ADC. Suppose that a normal operating temperature of theAFE device is at 50° C. and the optimum sampling phase N_(phase) of theADC (103, 113, 123) is the 15^(th) sampling phase (if there are totally32 sampling phases for each level). In addition, a normal full-scalevoltage of the ADC (103, 113, 123) is 1 volt and its bias current istypically 30 mA. The sensing-resultant signal S_(O) reflects atemperature magnitude measured by the temperature sensor 311. While thetemperature variation range of the AFE device 200 is within ±5° C., thetemperature compensation of the dynamic compensation circuit 312 willnot be launched. Instead, if the temperature of the AFE device 200 goesup more than 5° C. (e.g., at 60° C.), both the full-scale voltage andthe bias current of the ADC (103, 113, 123) will be getting lower due toa worse characteristic of the ADC (103, 113, 123); furthermore, theoptimum sampling phase N_(phase) is shifted from the 15^(th) samplingphase to the 13^(th) sampling phase, rendering images of the displaysystem unstable or fluctuating. At this moment, after receiving thesensing-resultant signal S_(O), the dynamic compensation circuit 312looks up corresponding parameters in the temperature compensation table400 with respect to the current temperature (60° C.). The correspondingparameters include a new optimum sampling phase N′_(phase) equal to thecurrent optimum sampling phase N_(phase) plus two and the full-scalevoltage and the bias current of the ADC (103, 113, 123) respectivelyadded up to 1.1V and 35 mA. Next, based on the obtained correspondingparameters, the dynamic compensation circuit 312 generates the firstcompensating signal C1 (to add two to the current optimum sampling phaseN_(phase)) and the second compensating signal C2 (to respectively pullthe full-scale voltage and the bias current of the ADC (103, 113, 123)up to 1.1V and 35 mA) to set related registers of the bandgap voltagereference circuit 130 and the clock generator 140. As such, what isexpected is that the optimum sampling phase N_(phase) is added back tothe 15^(th) sampling phase and that the ADC (103, 113, 123) iscompensated for its worse characteristic, thus avoiding the thermaldrift due to temperature changes.

It should be noted that the contents of the temperature compensationtable 400 vary according to the elements that are expected to improvethe thermal drift. As to the example given in FIG. 4, the elements thatare expected to improve the thermal drift are the clock generator 140and the ADC (103, 113, 123). If the element that is expected to improvethe thermal drift is the input buffer 102, the dynamic compensationcircuit 312 utilizes the second compensating signal C2 to set therelated registers of the bandgap voltage reference circuit 130 so as toadjust or compensate the gain or the offset voltage of the input buffer(102, 112, 122). In addition, the dynamic compensation circuit 312 canalso be implemented in hardware.

As to general display system controllers, the thermal drift is mostobvious in a LCD controller with a SOG circuit. While the thermal driftin the SOG circuit occurs, the DC level of the SOG circuit continuouslymoves up and down to cause the HS signal to vary. This may even resultin a shifted optimum sampling phase or an unstable or fluctuating image.Therefore, the improving effect of the invention which is applied to theLCD controller with the SOG circuit is most remarkable. FIG. 5 shows ablock diagram of an AFE device with temperature compensation accordingto a second embodiment of the invention. An AFE device with temperaturecompensation 500, which is disposed in a LCD controller, comprises a SOGcircuit 510, a temperature compensation circuit 210, a bandgap voltagereference circuit 130, a clock generator 140 and three convertingcircuits 150. The three converting circuits 150 respectively receive andconvert three analog signals R, G, SOG(=G+HS+VS) into three digitalsignals D1, D3, D2. Wherein, one of the three converting circuits 150and the SOG circuit 510 simultaneously the receive the SOG signal;moreover, the SOG circuit 510 extracts a (HS+VS) signal from the SOGsignal and then delivers the (HS+VS) signal to the clock generator 140for further processing. The same numerals as used in FIG. 2 are used todesignate the same elements and the description thereof is omitted. Inthis embodiment, the contents of the temperature compensation table 400can be adjusted such that the dynamic compensation circuit 312 canutilize the second compensating signal C2 to set the related registersof the bandgap voltage reference circuit 130 so as to adjust orcompensate the voltage of the SOG circuit 510, thereby solving oravoiding the thermal drift due to temperature changes.

Although the AFE device in the display system controller is taken as anexample, the temperature compensation circuit of the invention isapplicable to other analog application devices, such as amplifiers,ADCs, digital to analog converters, or voltage regulators. Analogcircuits are used to process analog signals and require a more accuratereference voltage or a more accurate clock signal to stabilize theoverall circuit. Therefore, it still falls within the scope of theinvention to make use of the temperature compensation circuit forcompensating the reference voltage or the accurate clock signal in orderto minimize the thermal drift in the analog application devices.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention should not be limited to the specific constructionand arrangement shown and described, since various other modificationsmay occur to those ordinarily skilled in the art.

1. An analog front end device, comprising: a reference voltage generatorfor generating a reference voltage; a clock generator for generating aclock signal; a damper for adjusting a DC level of an analog signal togenerate a second analog signal; a buffer for buffering the secondanalog signal to generate a buffering signal; an analog to digitalconverter receiving the reference voltage and the clock signal forconverting the buffering signal into a digital signal; and a temperaturecompensation circuit for providing a compensating signal to at least oneof the reference voltage generator and the clock generator.
 2. Theanalog front end device according to claim 1, wherein the clockgenerator receives either a horizontal sync signal or a vertical syncsignal to generate the clock signal.
 3. The analog front end deviceaccording to claim 1, which is disposed in a liquid crystal displaycontroller.
 4. The analog front end device according to claim 1, whichis disposed in a video decoder.
 5. The analog front end device accordingto claim 1, wherein the compensating signal further comprises a firstcompensating signal and a second compensating signal, and wherein thereference voltage generator adjusts the reference voltage according tothe first compensating signal and the clock generator adjusts the clocksignal according to the second compensating signal.
 6. The analog frontend device according to claim 1, wherein the temperature compensationcircuit comprises: a temperature sensor for sensing a temperature togenerate a sensing signal; and a dynamic compensation circuit forgenerating the compensating signal according to the sensing signal. 7.The analog front end device according to claim 6, wherein the dynamiccompensation circuit is implemented in either firmware or hardware byusing a lookup table.
 8. The analog front end device according to claim6, wherein the compensating signal sets the reference voltage generatorto adjust a full-scale voltage of the analog to digital converter whenthe temperature varies over a threshold value.
 9. The analog front enddevice according to claim 6, wherein the compensating signal sets thereference voltage generator to adjust a bias current of the analog todigital converter when the temperature varies over a threshold value.10. The analog front end device according to claim 6, wherein thecompensating signal sets the reference voltage generator to adjusteither a gain or an offset voltage of the buffer when the temperaturevaries over a threshold value.
 11. The analog front end device accordingto claim 6, wherein the compensating signal sets the clock generator toadjust a sampling phase of the analog to digital converter when thetemperature varies over a threshold value.
 12. The analog front enddevice according to claim 6, comprising: a Sync-on-Green circuit,receiving a Sync-on-Green analog signal, for extracting a sync signal togenerate a horizontal sync signal and a vertical sync signal.
 13. Theanalog front end device according to claim 12, wherein the compensatingsignal sets the reference voltage generator to adjust a voltage of theSync-on-Green circuit when the temperature varies over a thresholdvalue.
 14. An analog application device, comprising: a reference voltagegenerator for generating a reference voltage; a clock generator forgenerating a clock signal; an analog circuit receiving at least one ofthe reference voltage and the clock signal for processing an analogsignal to generate an output signal; and a temperature compensationcircuit for generating a compensating signal to at least one of thereference voltage generator and the clock generator according to atemperature in the analog application device.
 15. The analog applicationdevice according to claim 14, wherein the analog circuit comprises: adamper for adjusting a DC level of an analog signal to generate a secondanalog signal; a buffer for buffering the second analog signal togenerate a buffering signal; and an analog to digital converterreceiving the reference voltage and the clock signal for converting thebuffering signal into a digital signal.
 16. The analog applicationdevice according to claim 14, wherein the temperature compensationcircuit comprises: a temperature sensor for sensing the temperature inthe analog application device to generate a sensing signal; and adynamic compensation circuit for generating the compensating signalaccording to the sensing signal.
 17. The analog application deviceaccording to claim 16, wherein the dynamic compensation circuit isimplemented in either firmware or hardware by using a lookup table. 18.The analog application device according to claim 16, wherein thecompensating signal sets the reference voltage generator when at thetemperature varies over a threshold value.
 19. The analog applicationdevice according to claim 16, wherein the compensating signal sets theclock generator when the temperature varies over a threshold value. 20.The analog application device according to claim 14, wherein the analogcircuit is a voltage regulator.